1. Field of the Invention
The invention in general relates to the fabrication of layered superlattice materials, and more particularly to fabrication processes that provide low fatigue ferroelectric and reliable high dielectric constant integrated circuit devices that are unusually resistant to degradation.
2. Statement of the Problem
Bulk ferroelectric layered perovskite-like superlattice materials are known as phenomenonological curiosities. These materials comprise a broad class of ferroelectrics, and were reported by G. A. Smolenskii, V. A. Isupov, and A. I. Agranovskaya in Chapter 15 of the book, Ferroelectrics and Related Materials, ISSN 0275-9608, [V.3 of the series Ferroelectrics and Related Phenomena, 1984] edited by G. A. Smolenskii. As is understood in the art, these materials typically include an oxygen octahedral positioned within a cube formed of A-site metals at the cube corners with the oxygen atoms occupying the planar face-centers of the cube and a B-site metal occupying the center of the cube. These materials have previously not been considered to be useful as thin-film components for integrated circuits due to rapid polarization fatigue in thin-films and the high temperatures that are required to anneal a mixture of powdered superlattice-forming metals into an ordered superlattice.
Rapid thermal processing and furnace annealing in an atmosphere of oxygen are several of many processes that are well-known in the thin-film fabrication technology, See for example, "Process Optimization and Characterization of Device Worthy Sol-Gel Based PZT for Ferroelectric Memories", B. M. Melnick, J. D. Cuchiaro, L. D. McMillan, C. A. Paz De Araujo, and J. F. Scott in Ferroelectrics, Vol 109, pp. 1-23 (1990). It is also known to add excess lead in fabricating PZT using a spin-on and annealing process to account for lead lost as lead oxide vapor in the fabrication process. See U.S. Pat. No. 5,028,455 issued to William D. Miller et al. It is also known to add excess Bi.sub.2 O.sub.3 when fabricating a bismuth titanate thin film using sputtering to compensate for the loss of this component in the sputtering process. See "A New Ferroelectric Memory Device, Metal-Ferroelectric-Semiconductor Transistor", by Shu-Yau Wu, IEEE Transactions On Electron Devices, August 1974, pp. 499-504. E. C. Subbarao, in "A Family of Ferroelectric Bismuth Compounds", J. Phys. Chem. Solids, V. 23, pp. 665-676 (1962), discloses the creation of solid solutions of some layered superlattice materials and that several of their physical parameters, i.e., the dielectric constant and Curie temperature change as the proportions of the various elements comprising the solid solution change.
Hundreds of processes and parameters can potentially can affect the quality of a ferroelectric material. Those skilled in the art have been searching for more than thirty years to develop ferroelectric materials with properties of extremely low fatigue rates and polarizabilities as high as 25.